Several recent standards address virtual containers for rich multimedia content: collections of media with metadata describing the relationships between them and providing an immersive user experience. While these standards - which include MPEG-21 and TVAnytime - provide numerous tools for interacting with rich media objects, they do not provide a framework for streaming or delivery of such content. This paper presents the bitstream binding language (BBL), a format-independent tool that describes how multimedia content and metadata may be bound into delivery formats. Using a BBL description, a generic processor can map rich content (an MPEG-21 digital item, for example) into a streaming or static delivery format. BBL provides a universal syntax for fragmentation and packetization of both XML and binary data, and allows new content and metadata formats to be delivered without requiring the addition of new software to the delivery infrastructure. Following its development by the authors, BBL was adopted by MPEG as Part 18 of the MPEG-21 Multimedia Framework.